(1) Field of the Invention
The present invention relates to a draw-ironed metal vessel having a circumferential side seam. More particularly, the present invention relates to a novel draw-ironed metal vessel of excellent quality as having the combination of pressure resistance, the light-weight characteristic and the shock resistance.
(2) Description of the Prior Art
So-called draw-ironed cans are widely used for contents having a spontaneous pressure, such as beer and carbonated drinks.
These draw-ironed cans are prepared by draw-forming a metal blank punched in a disc or the like between a drawing punch and a drawing die to form a cup and ironing the side wall of the formed cup between an ironing punch and an ironing die to reduce the thickness of the side wall.
In a draw-ironed can, reduction of the side wall of the vessel is preferred for reducing the weight per unit volume of the can and decreasing the cost of the metal blank necessary for the production of the can.
However, this requirement has not been completely satisfied in the prior art because various limitations are placed on the production of cans. For example, when the thickness of the side of a can body is reduced, the buckling strength should naturally be reduced. When a can end is double-seamed to a can body, the axial load to be applied to the can body by a double seamer is 120 to 200 Kg, and if the thickness of the side wall portion is reduced below a certain limit, double-seaming of a can end becomes difficult.
The structurally weakest portion of a draw-ironed can is the portion double-seamed to a can end, and when the can receives shocks upon falling or the like, this portion may be broken and leakage may be caused in this portion.